Rotary pump



1M im@ 2g, w30. R. SCHMIDT l 1,771,863

ROTARY PUMP? v Filed Feb 2:5. 192s l; .lill 51| l I Patented July 29, 193.0 j'

UNrruD sra-TES PATENT orifice :RUDOLF semanal', or VIENNA, AUSTRIA, AssreNon 'ro rarraearArENrvEnwEa'r- Unes- UND INDUsram-Ax'rmNensELLscHArr, or vAnUz (Lmcn'rmrsrnm) ROTARY rUMP pplicatlon led February 23, 1928, Serial No. 258,438, andin Austria J'une 3, 1927.

in a maner somewhat analogous to the operap tion of gears with `one or two teeth.

In actual ractice, rotary pumps of the type to whicg the present lnvention relates have heretofore'been limited to pumps in which the pistons are provided with alternate, concave and convex portions which are caused to rotate relatively to each other in such a maner that the convex portion of one piston co-operates with,` the concave ortion of the other piston. Examples of suc Vtypes of rotary pumps are the well known Roots blowers and gear pumps. When the pump pistons are provided with these concave and convexportions, a squeezing of the 'fluid between such portions of thepump is produced in actual operation with consequent sudden l increases and resultant heavy radial stresses on' the shafts of the pistons. These objectionable phenomena are greatly ymagnified with increased rotary speed of the pistons and as a result of these phenomena as well as of the very pronounced' lack of uniformity of delivery, the operation of suchrotary machinesis impossible at the high operating speeds required in modern engineering practice.

In addition to `the rotary piston type of pump, there is employed in actual practice rotary pumps of the type known in the art as centrifugal pumps, and while the centrifuA al type pump may be operated at high v spee s, its use is confined .largely to the pumping of gases because 'of the fact that the...centrigufal 'pump is not capable of producing what may be termed a positive suction. While centrifugal pumps are sometimes employed for the pumping of liquids,

it is'necessary to provide special primingn means in order to secure a continuous column of liqud in the pump uponthe starting therel of. Moreover, 'centrifugal pumps can not be successfully employed for the pumping of viscous liquids, nor can they be used for high pressures. The princi al object of the .present invention is to prov e a new and improved construction for ya rotary pumping machine whereby the objectionable features heretofore present in pumpsof this type are obviated and whereby the pump may be used not-only at high rotative speeds but where it may be also employed to generate pressures retofore obtainable only with pumps of the reciprocating type. The essential feature of the pump which forms the subject matter of the present invention residesA in the provision of a pair of, cam-shaped pistons, thecross-sectional profile of which consists of cencentric, circular portions, joined by intermediate curves in such a manner that the entire proileof, each cam is free from concave portions an'd the pair of pisonts co-operate with each other without con- Figure 1 of the accompanying drawings is a diagram representing vthe invention. Figure 2 is a; vertical axial section of a pump 'with one pair of pistons according lto the invention the sectlon bein taken on line w y (Figure 3). Figure 3 1s a cross section of the pump shown in Figure 2.l Figure 4 represents a vertical axial section through va pump with two pairs of pistons.

In F-igure 1 G -g denote'the double casing of the rotary pump with a cylindrical bore; K is a cam shaped piston of large cross'section rotating on axis' c in direction of arrow.; a cam,l shaped piston of considerably smaller cross section, rotating on axis o1 in the opposite direction. Each of the two cam shaped pistons K and k together withthe corresponding portions of the double casing as well as` with a portion of the profile of its cooperating piston, forms an individual, rotary pump with a crescent-shaped working chamber the effective portion of which during each revolution of the piston changes periodically. Both rotary pumpshave sucl cave portions. In the larger piston K the tion pipe S and delivery pipe D in common.- In order to avoid any interruption of the uniform operation .of the pump, both cam 'shaped pistons must revolve at equal angular flo velocities and at the same time by continually converging upon each other with an intermediary film of liquid sealingthe points of convergence, must shut olf suction pipe S from de iver'y pipe D.

' The cross-sectional profile of each piston, as clearly shown in Fig. 1, consists of a pair or. .diametrically opposed, concentric, y cirvcular portions which are joined by intery'mediate curves in such a-manner that the entire prole of each piston is free from condiametrically opposed, concentric, circular portions are included between the points M, N and M', N', while the intermediate curved portions are included between the points M, M and N, N', while in the smaller piston c the opposed, circular portions are included .between the points m, mm', n', and the intermediate curves between lm, m and n, n".

In order to avoid any jamming which might otherwise occur with profiles of this type, the pistons co-operate with one another without actual contact at their points of maximum convergence and-with an "accurately determined amount of play just sufficient to avoid actual contact but to permit the presence of the intermediary sealing film. of liquid above referred to.

The construction of .the pistons is such that when each piston is in its zero position` i. e., with its larger radius, circular portion adjacent to thesuction and delivery ports,

and with the piston in a position such that it. vis symmetrically disposed with respect to a plan'passing through the axes of the pistons,

it must cut of its own working chamber from the delivery and intake pipe. This require ment is fulfilled .by an ample dimensioning of the angle@ corresponding to the concentric, circular portions M, N and m, n, respectively.

It will be seen by referring to Fig. 1 which shows the smaller piston c in its zero position, thatthe concentrlc portion m, n thereof 'eX- tendsA from the, edge of the suction port S to the edge of the delivery port D.' When the larger piston K is-in 'its zerol position (that is rotated through 180 from the position shown in Fig. 1.) `its circular portion M', N of its profile of large radius will extend from the lower edge of the suction port S to the lower edge of .the delivery port D, thereby sealing or cutting 0E communication between the suctlon and delivery sides of the lower worklng chamber.

" 'In order that the rotary pumpv may be capableof being rot-ated at high speeds it isl ofs the.. greatest importance that uniformde-- livery uring each rotation of. the ump be approxlmated as closely as possib e, or at least that sudden or marked variations in the pressure conditions be avo1ded.

These conditions are fulfilled if B+r=-c=constant if the thickness of the fluid film between the curved parts in neglected where vR or r denote the variable radii evident from the-l following consideration lIf piston K be turned in the direction of arrow (Figure 1) through angle (p, the radius of contact isincreased by an amount a resulting in a corresponding decrease of the amount of liquid drawn-in or delivered respectively at this moment. The radius of contact for the governin piston lo must, however, be decreased by the same amount a, resulting in a corresponding increase of the amount lofliquid drawn-in or delivered re- `spectivel by this piston,if/the equation- R-l-rB-is toY be fulfilled in the new relative position of both pistons. Moreover from this 1t follows that, if piston K be shaped in s uch a manner as to cover suctionand delivery-passages when in zero position, piston k will do likewise in its analogous .posiy tion. v

Accordingto Figures 2 and 3, the two pistons show the same dimensions. r l denotes the casing commonto both pistons 2 and 3, 4 is the suction branch and 5 the delivery branch. Piston 2 is mounted on a driving shaft 6, which runs in 'ball-bearings 7 and 8. 9 is a pinion keyed on to a shaft, gearing with a .pinion 10 of the same diameter and withvthe same number Vof teeth, which itself is keyed ontothe shaft 11 with piston 3. 12 and 13 are ball-bearings for shaft 11.

In order to ensure a more efective lateral packing,

pistons 2 and 3 and the Aside walls of the casing, butting agamst the end walls of thecasing by means of p 'ckin the casing may, if desired, be provided with liners 14 and 15 arranged between.

rings 16. The spaces 20, enclosed by e side Walls of casing and liners, onboth sides, are connected with fl the delivery/side of the rotary pump by ducts 21 (-F1gure'2.) With the resulting effect that I the liners are continually pressedagainst the cheeks of both pistons, automatically adjusting themselves under the ressure of the liquid by moving inwards should they them-V v selves or the pistons experience any wear.v

If a certainA contourline be chosen for pis- :ton K (Figure 1) resulting in producing for perfectly uniform pump output with a doublepisto'n, 3* rotating in the opposite direction on shaft 11 lhaving analogous eccentricities also set at 180.

A rotary pump having a single pair of pistons (Figures 2 and 3), however, will, in conjunction with its counter-piston of equal dimensions," ensure approximately constant pump output without the shape of the pisl ton strictly complying with the equation QI+QH=constant for two diametrically opposed positions. This result will be apparent from the following consideration Piston 3 will act for piston 2 as the separating medium between suction side and delivery side, and vice versa. At equal radius the output of each piston is proportional to theradial distance of the point of contact with the counter-piston from tne circumference of the casing.

Since maximum convergence between both pistons 2, 3 occurs in the course ofa complete revolution within a zone adjacent to and delinitely fixed by the plane enclosing the two axes of rotation of both pistons, the point of maximum convergence between the two piston contours Will be moving up down closely adjacent to the centre-line c c during one revolution, and the sum of the two distances of the oint of maximum convergence from the circumferences of'both casings will practically be constant and equivalent -to the amount s (Figure 3) In the. construction of tlie rotary piston machine, in accordance with the principle of this invention, the shape of thevpistons is dependent upon the service requirements to be met. The relation of the angles of the concentric piston sections of the intermediate curved vsections of the piston proles is chosenin such af manner that the degree of inequality of delivery never produces a condition in service which would cause a break in the flow of the liquid handled.

I'claim:- v

1. A rotary pump of the type having 4a .pair of pistons-which co-operate inthe manner of'a single or double tooth gearing, characterized by each of said pistonshaving a cam-shaped profile comprisin a pair of concentric diametricallyxoppose circular sections connected by intermediary sections,

the intermediary sections merging gradually with the circular sections and the entire profile of each piston being free from concaved or recessed'portions..

2. A rotary pump of the type having a pair of pistons which cli-operate in the manner of a' single or double tooth gearing, characterized by each of said pistons having a cam-shaped profile comprising a .pair of concentric, diametrically opposed, circular sections connected by intermediary sections, the intermediary sections merging gradually with the circular' sections and the entire prol file .of each piston being free from, concaved or recessed portions, and means for rotating said .pistons at equal angular velocities, and the dimensions of the circular and curved sections of the profile of each piston, andthe v radii thereof with respect to their respective axes of rotation, being such that during each .rotation of each piston, maximum convergence, without actual contact of the piston profiles, occurs, wherebyl an intermediary film of liquid exists between the two pistons at their point of convergence and seals the suction from 4the delivery side of the pump.

3. A rotary pump .of the type having a pair of pistons which co-operate'in the manner of a single or double tooth gearing, characterized Aby each of said pistons having a cam-shaped profile comprising a pair o concentric, diametrically opposed, circular secf tions connected by intermediary sections,'the intermediary sections merging gradually with the circular .sections and the entire profile of each piston being free from concaved or recessed portions, one of the .circular sections of each piston being of larger radius than its opposed circular section and the inj eluded angle of said larger circular section being sufliciently large to cause. said section, when eachI piston is in zero position with its `larger section adjacent to its suction and delivery ports, to extend from the suction to the delivery port and thereby shut 0E communication between such ports.

4. In a rotarypump of the type wherein a pair oflcam-shaped pistons are rotatable v I in a pump casin and operate in the manner of single or dou le tooth gearing, each piston having a profile consisting of a pair of concentric circular sections of i and intermediate sections connecting and merging gradually with said circular sec-l tions in such a'manner that the entire profile of each piston is free from concaved o r recessed portions, the radius R of one piston at ever point of its profile being predetermined y the 'adius of the other piston .rp at such point substantially in accordance with the formula R+r=a constant, and so that an accurately predetermined amount of play is provided etween the pistons at their4 int ofconvergence suiiicient to prevent ]amming of the pistons in their rotaferent radii, l

tion and to insure the presence of an intermediary film of sealing liquid between said pistons and at their points of convergence. 5. A rotaryr pum of the type having a 5 pair of pistons Whic co-operate in the manner of al single or double toothgearing, characterized by each of said pistons having a cam-shaped profile comprising a pair of concentric diametrically opposed, circular secl m tions connected by intermediary sections, the

intermediary sections merginggradually l with the circular sections and the entire prole vof each piston being free from abrupt, concavedor recessed portions. In testimony whereof I aix my signature.

. RUDOLF SCHMIDT. 

